Biosorption of Cr (III) from Polluted Water Using Pennisetum clandestinum Hochst (Kikuyo)

Given the abundance of kikuyu biomass resulting from the pruning of green areas, the aim of this study was to evaluate its use as a biosorbent (BK) for Cr (III) removal from polluted waters. The biomass was activated using H₂SO₄ (1.25%) and NaOH (3.25%). The characterization methods were Fourier-Transform Infrared Spectroscopy (FTIR), scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), and Brunauer-Emmett-Teller (BET) analysis. Our results confirmed the presence of active groups on BK, such as -OH, -C=C-, -C=O, and -C-O-, with an increase of 1308.58% in specific surface area, as well as the presence of chromium on the biosorbent after adsorption process. The adsorption capacity (q) was tested in a jar test as a function of biomass granulometry, dose (BK), and the pH of the solution; the best response was 47.9 mg/g at a pH of 5.5, a biosorbent dose of 0.5 g/L, and a biosorbent size of 100 μm. The effect of pH was positive; by increasing the pH, the adsorption capacity increased. However, the effect of the biosorbent dose and size was negative, as when increasing the dose and granulometry, the adsorption capacity decreased. In addition, the kinetic process was studied, where the removal data were better fitted for the pseudo-second-order kinetic model, confirming that the adsorption mechanism was chemisorption. The adsorption capacity was 37.6 mg/g for industrial wastewater. The possibility of using kikuyu within the circular economy was demonstrated and suggests its application in continuous systems for real-world environmental conditions.